The problem with the WT interpretation of kat'oikon cannot be simply be solved by determining a general "distributive" use of kata + accusative. For in the NT this particular expression clearly refers, in a semi-technical way, to communitarian meetings in private homes of wealthy Christian patrons hosting the ekklèsia, or part of it. Cf. its use in Romans 16:5; 1 Corinthians 16:19; Colossians 4:15; Philemon 2 which is neither "distributive" nor "consecutive" as it refers to one place of meeting in every instance.
In Acts this expression is both parallel and contrasted with to hieron, "the temple" (2:42), for the "breaking of bread," or ritual communitarian meal; the same parallel and contrast is found in 5:42 for equally collective teaching and preaching.
The same can be said of the plural form kat[a tous] oikous: this is where Saul looks for and finds the ekklèsia (8:3) -- he doesn't go from door to door in the whole city, nor even looks for every private Christian home, but targets the places of meetings. This is where Paul taught, not unbelievers but the elders of the ekklèsia in Ephesus(20:20).
Undoubtedly unbelievers could join the "services" of the ekklèsia kat'oikon (as is implied in 1 Corinthians 14:23, for instance), but it is absolutely ludicrous to isolate this expression from its overall NT contexts and imagine it depicts the apostles knocking at the homes of unbelievers to preach the Gospel privately to each and every one of them.
Incidentally Luke has a different expression for "from house to house" (ex'oikias eis oikian) in Luke 10:7, pointing to what the missionaries should not do (changing hosts in the same town).
